c# - 使用正确的换行符将 HTML 转换(呈现)为文本

Question

我需要将 HTML 字符串转换为纯文本(最好使用 HTML Agility pack)。使用适当的空格，尤其是适当的换行符。

“适当的换行符”是指这段代码:

<div>
    <div>
        <div>
            line1
        </div>
    </div>
</div>
<div>line2</div>

应转换为

line1
line2

即只有一个换行符。

我见过的大多数解决方案只是简单地转换所有 <div> <br> <p>标记为 \n很明显，s*cks。

对于 C# 的 html-to-plaintext 渲染逻辑有什么建议吗？不是完整的代码，至少像“用换行符替换所有关闭的 DIV，但前提是下一个兄弟也不是 DIV”这样的常见逻辑答案确实有帮助。

我尝试过的事情:简单地得到 .InnerText属性(显然错误)，正则表达式(缓慢，痛苦，很多黑客，正则表达式比 HtmlAgilityPack 慢 12 倍 - 我测量过)，这个 solution 和类似的(返回更多的换行符然后需要)

Answer 1

下面的代码与提供的示例一起正常工作，甚至可以处理一些奇怪的东西，例如 <div><br></div> ，还有一些需要改进的地方，但基本思想是存在的。查看评论。

public static string FormatLineBreaks(string html)
{
    //first - remove all the existing '\n' from HTML
    //they mean nothing in HTML, but break our logic
    html = html.Replace("\r", "").Replace("\n", " ");

    //now create an Html Agile Doc object
    HtmlDocument doc = new HtmlDocument();
    doc.LoadHtml(html);

    //remove comments, head, style and script tags
    foreach (HtmlNode node in doc.DocumentNode.SafeSelectNodes("//comment() | //script | //style | //head"))
    {
        node.ParentNode.RemoveChild(node);
    }

    //now remove all "meaningless" inline elements like "span"
    foreach (HtmlNode node in doc.DocumentNode.SafeSelectNodes("//span | //label")) //add "b", "i" if required
    {
        node.ParentNode.ReplaceChild(HtmlNode.CreateNode(node.InnerHtml), node);
    }

    //block-elements - convert to line-breaks
    foreach (HtmlNode node in doc.DocumentNode.SafeSelectNodes("//p | //div")) //you could add more tags here
    {
        //we add a "\n" ONLY if the node contains some plain text as "direct" child
        //meaning - text is not nested inside children, but only one-level deep

        //use XPath to find direct "text" in element
        var txtNode = node.SelectSingleNode("text()");

        //no "direct" text - NOT ADDDING the \n !!!!
        if (txtNode == null || txtNode.InnerHtml.Trim() == "") continue;

        //"surround" the node with line breaks
        node.ParentNode.InsertBefore(doc.CreateTextNode("\r\n"), node);
        node.ParentNode.InsertAfter(doc.CreateTextNode("\r\n"), node);
    }

    //todo: might need to replace multiple "\n\n" into one here, I'm still testing...

    //now BR tags - simply replace with "\n" and forget
    foreach (HtmlNode node in doc.DocumentNode.SafeSelectNodes("//br"))
        node.ParentNode.ReplaceChild(doc.CreateTextNode("\r\n"), node);

    //finally - return the text which will have our inserted line-breaks in it
    return doc.DocumentNode.InnerText.Trim();

    //todo - you should probably add "&code;" processing, to decode all the   and such
}    

//here's the extension method I use
private static HtmlNodeCollection SafeSelectNodes(this HtmlNode node, string selector)
{
    return (node.SelectNodes(selector) ?? new HtmlNodeCollection(node));
}